1. Field of the Invention
This invention relates to a non-contact positioning apparatus and method suitable particularly, but not exclusively, for positioning a surface working, testing or inspection device relative to a surface to be worked, tested or inspected at a desired position and orientation relative thereto.
2. Discussion of Prior Art
Conventional techniques used in aircraft wing assembly include the use of drilling templates to define hole positions therealong for components such as fasteners. Frequently, additional tooling is required to ensure that the holes are drilled normal to the wing surface, each of which holes is drilled by a worker and requires considerable skill to achieve the required tolerances. Once inserted into their designated hole location, if the fasteners protrude from the wing skin, an additional operation is required to remove the protruding part. As tolerances are typically tighter than 0.5xc2x0 off normal, the number of holes failing to meet the specifications can be significant. Current practice is thus costly in terms of the additional tooling set up time, drilling time and costs of parts. Various non-contact measurement systems have been developed in an attempt to address these issues, concentrating on measuring the orientation and position of the surface to be worked relative to a working component. Specifically, laser line rangefinders have been used to project a cross-hair onto a surface and the angle between the two cross-hair arms provides information regarding the orientation of the surface relative to rangefinder arrangement. However, the non-Gaussian spread of the laser line has proven to be significant, reducing the ability of the system to measure the surface position and orientation and thus failing to satisfy tolerancing requirements. A system including four lasers in an integrated unit has also been developed, which lasers project laser spots on a surface. The spots are imaged using a single camera to measure the relative spot centre positions and the degree of ellipticality thereof. In this case the accuracy and functionality are limited by the proximity of the laser spots within the integrated unit.
There is therefore a need for a device positioning apparatus which enables accurate positioning of a device relative to a surface within a specified tolerance, reduces extraneous procedures and components on the wing surface, and reduces the time taken to perform the drilling operation.
According to a first aspect of the present invention there is provided a non-contact apparatus for positioning a surface working, testing or inspection device relative to a surface to be worked, tested or inspected at a desired position and orientation relative thereto, including a baseplate locatable at a distance away from the surface, means for mounting the surface working, testing or inspection device on the baseplate, three or more range finder units removably mounted in spaced array on the baseplate, each of which units includes a source for impinging a beam of electromagnetic radiation on the surface, and a detector for imaging the impinging radiation and for calculating a distance measurement from a datum location on the respective source to a point corresponding to the surface beam impingement, the apparatus also including transformation means for translating each of said range finder distance measurements into a common baseplate co-ordinate frame of reference, a processor for receiving and processing the distance measurements to establish therefrom a first orientation and position of the surface relative to the baseplate, and thus to the surface working, testing or inspection device when mounted thereon, and indexing means in operative association with the processor for positioning the baseplate and surface working, testing or inspection device when mounted thereon at the desired position and orientation relative to the surface.
Preferably the means for mounting the surface working, testing or inspection device on the baseplate includes at least four equi-spaced holes through the baseplate, at least four externally threaded shank bolts locatable through said holes, and a substantially rigid removable housing attachable to the surface working, testing or inspection device, which removable housing is a hollow cylinder with at least one end partially open, which partially open end has at least, four transverse internally threaded equi-spaced holes for threadable engagement by said shank bolts for securing the housing to the baseplate.
Conveniently the transformation means includes mapping vector means operable to provide a position mapping vector and a direction mapping vector for each of the range finders, which position mapping vectors describe each range finder datum location by axial, transverse and perpendicular components in the baseplate co-ordinate frame of reference, which baseplate co-ordinate frame is characterised by axial, transverse and perpendicular orthogonal axes, and which direction mapping vectors describe the normality of each range finder sensor relative to the surface to be worked, tested or inspected by vectoral axial, transverse and perpendicular components in the baseplate co-ordinate frame of reference.
Advantageously the mapping vector means includes a substantially rigid, substantially planar calibration plate locatable at an array of calibration positions between the baseplate and the surface, which calibration plate is, at each of the calibration positions, located substantially parallel to the baseplate, gauge blocks of a pre-determined thickness locatable between the baseplate and the calibration plate, which gauge blocks provide means for determining the axial components of the position mapping vectors, and a surface measuring instrument, which surface measuring instrument provides means for determining the transverse and perpendicular components of the position mapping vectors and thence the direction mapping vectors.
Preferably there is a series of communication links between the processor and each range finder unit for receiving the distance measurements, which links include a control box in operative association with a power supply, which control box is operable to sample the range finder distance measurements at a desired rate, a multi-core cable connecting the range finder unit to the control box, and a serial cable connected between the control box and the processor for communicating the sampling rate to the control box.
Conveniently the indexing means includes a robotic arm having six servo motors attached thereto, which arm is rigidly connected to the removable housing and thereby to the surface working, testing or inspection device when attached thereto, a robot controller for controlling the servo motors, which robot controller is connected to the processor by a serial cable for receiving therefrom a 4xc3x974 (four row four column) homogenous matrix describing a rotation and translation required to position the baseplate and thereby the surface working, testing or inspection device when mounted thereon, at the desired position and orientation relative to the surface to be worked, tested or inspected.
Advantageously the baseplate is a substantially rigid substantially regular hexagonal plate with a hole therethrough substantially in the centre thereof, which hole is of sufficient diameter to allow any axially protruding parts of the surface working, testing or inspection device to pass therethrough when the surface working, testing or inspection device is attached to the substantially rigid removable housing and thence to the baseplate.
Preferably each of the three or more range finder units is attachable to an outer perimeter of the baseplate by bolt means, and wherein the units are equi-spaced therearound.
Conveniently each range finder unit has a radiation source with a laser spot of 635 nm wavelength.
Advantageously the surface working, testing or inspection device is a drill.
Preferably the surface working, testing or inspection device is a welding torch.
Conveniently there are four range finder units.
According to a further aspect of the present invention there is provided a method for positioning a surface working, testing or inspection device relative to a surface to be worked, tested or inspected at a desired position and orientation thereto, in which the surface working, testing or inspection device is mounted on the baseplate locatable at a distance away from the surface, three or more range finder units are removably mounted in spaced array on the baseplate, each of which units includes a source of electromagnetic radiation and a detector for the radiation, a beam of said radiation is impinged by each unit on the surface, imaged by the detectors and used to calculate a distance measurement from a datum location on the respective source to a point corresponding to the surface beam impingement, each of said range finder distance measurements is translated by transformation means into a common baseplate co-ordinate frame of reference, the distance measurements are processed by a processor to establish therefrom an orientation and position of the surface relative to the baseplate, and thus to the surface working, testing or inspection device mounted thereon, and the baseplate and surface working, testing or inspection device is positioned at the desired position and orientation relative to the surface by an indexing means in operative association with the processor.
Preferably the transformation means is operated to provide a position mapping vector and a direction mapping vector for each of the range finders, which position mapping vectors describe each range finder datum location by vector axial, transverse and perpendicular components in the baseplate co-ordinate frame of reference, and which direction mapping vectors describe the normality of each range finder sensor relative to the surface to be worked, tested or inspected by vectoral axial, transverse and perpendicular components in the baseplate co-ordinate frame of reference.
Conveniently the axial components of the position mapping vectors are determined from a geometric fit to a series of gauge block height measurements corresponding to the surface beam impingement distance measurements returned by each of the at least three range finder units, which beam impingement is provided by a substantially rigid calibration plate positioned substantially parallel to the baseplate, and which series of height measurements is provided by a positioning of the calibration plate at an array of calibration positions thereunder, and in which the transverse and perpendicular components of the position mapping vectors are determined from a regressive fit to an array of beam impingement points located in the plane of the calibration plate by a surface measuring instrument, which array of beam impingement points is provided by the array of calibration plate calibration positions.
Advantageously the distance measurements are processed by determining a first position and orientation of the surface working, testing or inspection device relative to the surface, determining a required translation and/or rotation of the surface working, testing or inspection device in the baseplate co-ordinate frame of reference in order to move said device to the desired position and orientation, and decoding the required translation and/or rotation of the surface working, testing or inspection device from the baseplate co-ordinate frame of reference into a co-ordinate frame of reference of the indexing means.
Preferably the first position and orientation is determined by forming a baseplate transformation equation for each range finder unit, which transformation equation combines each respective distance measurement with each of the position mapping vectors and the direction mapping vectors, thereby defining, for each of the range finder units in turn, co-ordinates of the respective surface beam impingement point in the baseplate co-ordinate frame of reference, combining the beam impingement points in the baseplate co-ordinate frame of reference by vectoral subtraction therebetween so as to provide at least two surface vectors, taking a cross-product of the at least two surface vectors so as to provide a vector normal thereto, and from thence a unit vector, and taking a scalar product of the vector normal and any one of said beam impingement points in the baseplate co-ordinate frame of reference so as to define a first position plane.
Conveniently the required translation and/or rotation is determined by processing a first transformation, which first transformation defines a translation and rotation from the first position and orientation to a temporary position and orientation, and a second transformation, which second transformation defines a translation and rotation from the temporary position and orientation to the desired position and orientation, and combining the first and second transformations by matrix multiplication of said first and the inverse of said second transformations to provide a standard 4xc3x974 (four row, four column) homogenous matrix describing the required rotation and translation in the baseplate co-ordinate frame of reference.
Advantageously the temporary position and orientation is defined by means of a temporary co-ordinate system, which temporary co-ordinate system is defined by an origin and orthogonal axial, transverse and perpendicular axes, which axial axis is given by the unit vector normal and which transverse axis is given by a cross-product of said unit vector normal and a main axis unit vector, which main axis vector is defined as equal to the axial axis of the baseplate co-ordinate frame and is constrained to pass through a single point corresponding to an average of the at least three range finder position mapping vectors, and which temporary co-ordinate system origin is given by an intersection of the main axis vector with the first position plane.
Preferably the first transformation translation is given by a 3-by-1 (three row, one column) translation matrix defined by translational components of a vector connecting an initial displacement from the surface to be worked, tested or inspected and the temporary co-ordinate system origin, which initial displacement is defined by the first position plane, and the first transformation rotation is given by a 3-by-3 (three row, three column) rotation matrix having the temporary co-ordinate system transverse axis as its first component, the temporary co-ordinate system axial axis as its third component and the cross product of said first and third components as its second component, and in which the second transformation translation is given by a 3-by-1 (three row, one column) translation matrix defined by translational components of a vector connecting the temporary co-ordinate system origin and a required displacement therefrom, which displacement is defined by a plane describing the desired position and orientation of the baseplate relative to the surface, and in which the second transformation rotation is given by a 3-by-3 (three row, three column) rotation matrix having the temporary co-ordinate system transverse axis as its first component, a unit vector normal to the desired position plane as its third component and a cross product of said first and third components as its second component.
Conveniently the required translation and/or rotation of the surface working, testing and inspection device in the baseplate co-ordinate frame of reference is decoded into the indexing means co-ordinate frame of reference by matrix multiplication of a baseplate to indexing means matrix mapping, the 4xc3x974 (four row, four column) homogenous matrix describing the required rotation and translation in the baseplate co-ordinate frame of reference, and the inverse of the baseplate to indexing means matrix mapping.
Advantageously the baseplate to indexing means matrix mapping translates the baseplate co-ordinate frame of reference into the indexing means co-ordinate frame of reference, which mapping is substantially constant.